ANGOLA
ZIMBABWE
SOUTH
AFRICA
GABON
CONGO
UGANDA
SUDAN
NIGERIA
KENYA
SOUTH
SUDAN
MALI
CÔTE
D’IVOIRE
(IVORY COAST)
GUINEA
LIBERIA
SIERRA
LEONE
DEMOCRATIC
REPUBLIC OF
THE CONGO
Lagos
Kikwit
Durba
Johannesburg
Port
Harcourt
Libreville
Nairobi
Kigali
Bouaké
Méliandou
Freetown
Monrovia
Conakry
Bamako
TAÏ NATIONAL PARK
AFRICA
SAHARA
Chinhoyi
Caves
Kitum
Cave
1976
318 cases
88% fatality rate
1976
284 cases
53% fatality rate
DENSE
FOREST
EQUATOR
EQUATOR
Range of Angolan
free-tailed bat
(Mops condylurus)
Range of Angolan
free-tailed bat
(Mops condylurus)
Cases26,018Deaths10,807
AN
ELUSIVE
ENEMY
No one knows for certain where the Ebola
virus lurks between outbreaks; it has never
been definitively tracked to a host species
in the wild. Transmission to humans has
been sporadic and extremely rare—but all
too often deadly. Fatality rates in some
outbreaks have reached 90 percent. Since
Ebola was discovered in 1976, population
growth in at-risk countries has nearly tripled,
and people have become more mobile.
LAUREN E. JAMES, EMILY M. ENG, AND JASON TREAT, NGM STAFF; MEG ROOSEVELT
SOURCES: WHO; CDC; IUCN; DAVID M. PIGOTT, UNIVERSITY OF OXFORD; GLOBAL
LAND COVER FACILITY; LANDSCAN
A Family of Viruses
Besides Ebola itself, which is responsible for most
outbreaks, four other viruses are recognized within
the ebolavirus group: Sudan, Taï Forest, Bundibugyo,
and Reston. All cause Ebola virus disease, except
Reston, which is probably harmless to humans.
Marburg, a closely related pathogen, was discovered
in 1967. Marburg virus disease is also often fatal.
The first outbreaks of Ebola virus
disease, in 1976, erupted simultane-
ously in what was then Sudan (now
South Sudan) and Zaire (now the
Democratic Republic of the Congo).
Human
Chimpanzee
Other
species
Gorilla
SUSCEPTIBLE SPECIES
SUSCEPTIBLE SPECIES
?
POSSIBLE RESERVOIRS
POSSIBLE RESERVOIRS
Insectivorous bats
Fruit bats
Unknown
?
The Path to Humans
Three bat species have long been suspected of har-
boring Ebola. But one theory suggests a two-host
system, in which the virus’s ultimate host—perhaps
some insect, tick, or other arthropod—must first in-
fect a bat or other mammal. The virus can then pass
to humans, typically when they handle bush meat.
2,000
3,000
1,000
100
Total cases or deaths
Less
More
Tree-cover density
Urban area
Ebola viruses 1976-2012
Current Ebola
Past cases
Marburg 1975-2012
Outbreaks
Cases
Deaths
0mi
200
0km 200